Specialty sorghums in direct-expansion extrusion

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Abstract

Whole-grain, high-fiber, or decorticated extrudates of excellent properties were
made from white (nonwaxy, heterowaxy, waxy) sorghums or brown tannin-sorghums.
Intact grains or prepared raw materials (cracked, cracked and sifted, decorticated) were
extruded in a high-temperature, short-time (HTST) extruder. Waxy extrudates expanded
less and were softer than those from nonwaxy or heterowaxy sorghums. Waxy
extrudates had bigger air cells and thicker cell walls. Low moisture used in this type of
extrusion and its interaction with the different amylose contents were the causes of the
differences. Whole-grain extrudates from white sorghum had similar sensory
acceptability to those from white decorticated sorghum. They had bland flavor and
appearance and texture characteristic of whole-grain products. Extrudates from tannin
sorghums were reddish brown due to their high levels of phytochemicals. The more
expanded, softer products from whole-grain tannin sorghum were obtained when the
grain was cracked and sifted. Decreased expansion was caused by higher levels of fiber
and greater particle sizes (as in the extruded intact grain), and by reduced particle sizes
(as in the cracked non-sifted grain). Expansion was correlated to smaller air cells with
smooth walls. A simple enzymatic method was developed that isolates the 'gritty'
particles from whole-grain/high-fiber extrudates, which closely correlated with
expansion. Gritty particles were fiber (bran) plus undegraded starchy material. Whole
grain/high fiber extrudates from white and tannin sorghums are an excellent option for
food processors because of their excellent taste, appearance and texture.